The goal of the research projects in this program project application is to elucidate the pathogenesis of GVHD and to develop new therapies designed to control GVHD while maintaining GVL. Important to the success of this project is the biostatistical collaboration with individuals in each of the 3 projects and the other Cores. The purpose of the Biostatistics Core is to provide the following services that will be utilized by all of the research projects included in this Program Project. 1. To provide biostatistical collaboration for clinical research protocols. This includes all aspects of design, conduct, analysis and reporting of the clinical protocols, and direction of data processing and quality control assurance. 2. To provide biostatistical collaboration for animal and laboratory research studies. This includes all aspects of design, conduct, analysis and reporting of such studies, including the coordination of laboratory results with parameters and outcomes from the clinical studies. 3. To supervise the data processing and data quality assurance, and to coordinate the efforts of the data coordinator and those of the data analyst in maintaining an accurate computerized database. 4. To provide computing resources for data processing, forms design, statistical analysis, standardized reporting, and quality control.